1. Field of the Invention
The present invention relates, generally, to a high pressure fuel injector for internal combustion engines. More specifically, the invention relates to a fuel injector which employs a shape memory alloy to plug a high pressure fuel passage and a method of manufacturing same.
2. Description of the Related Art
Fuel injector assemblies are employed in internal combustion engines for delivering a predetermined, metered amount of fuel to the combustion chamber at preselected intervals. In the case of compression ignition, or diesel engines, the fuel is injected into the combustion chamber at relatively high pressures. Presently, conventional injectors are delivering this fuel at pressures as high as 32,000 psi. These are fairly high pressures and have required considerable engineering attention in ensuring structural integrity of the injector, good sealing properties, and effective atomization of the fuel within the combustion chamber. However, increasing demands on greater fuel economy, cleaner burning, fewer emissions, and No.sub.x control have placed, and will continue to place, even higher demands on the engine's fuel delivery system including increasing the fuel pressure within the injector.
Fuel injectors presently employed in the related art typically include a high pressure fuel passage which extends between a solenoid actuated control valve and the plunger cylinder in the injector body. Fuel at relatively low pressure is supplied to the control valve which then meters the delivery of the fuel at predetermined intervals through the high pressure fuel passage to the plunger cylinder. The fuel ultimately exits the injector through a fuel nozzle.
The high pressure fuel passage is often formed in the injector body by drilling a hole from one side of the injector body through a chamber formed to accommodate the structure of the control valve and between the control valve and the plunger cylinder. The opening in the side of the injector body formed from the drilling is then sealed with a steel plug through a brazing operation. One of the disadvantages with this arrangement is that the brazed plug requires expensive tools and tapered hole machining during the manufacturing process and expensive metal removal after the high temperature braze and hardening process. Further, as the demand for higher fuel injection pressure has increased, the reliability of brazed plugs in this environment has not always met the high manufacturing quality standards required in the relevant industries. More specifically, the brazed plugs can leak and even fail under the high injection pressures. Further, both the plug and the fuel passage are subjected to cyclical pressures ranging between 0 and the peak stress generated by the fuel pressure. The alternating stress amplitude adversely effects the fatigue life of the injector body and can result in early failure through body cracks.
Thus, there is a need in the art to provide a better seal for the high pressure fuel passage of a fuel injector which reduces costs by eliminating the brazing process presently employed in the related art and while providing a very secure, tight seal at the open end of the high pressure passage that resists leaking, even under very high pressures. Further, there is a need in the art for a sealing mechanism in this environment which reduces the stress amplitude on the injector body generated in the high pressure fuel passage.